(Sorry for that long title)
For me personally, it's the lack of online capabilities. There are so many games nowadays that have most, if not all of the gameplay focused online, and that feels very temporary to me. Online servers are always going to go down eventually, whereas retro games are permanent and will be just as playable in the current decade as they were in the '80s and '90s. In a few years certain online focused games are going to be literally unplayable.
For me personally, it's the lack of online capabilities. There are so many games nowadays that have most, if not all of the gameplay focused online, and that feels very temporary to me. Online servers are always going to go down eventually, whereas retro games are permanent and will be just as playable in the current decade as they were in the '80s and '90s. In a few years certain online focused games are going to be literally unplayable.